The eastern theatre of the war has been described in a preceding chapter and it will be recalled that for about two hundred miles from east to west Russian Poland is inclosed on the north by East Prussia and on the south by Austria. Moreover, the Sudetic Mountains on the Austrian frontier and the huge forests of Poland protect the position of German Silesia southeast of Breslau. Passing through it are the chief lines of railway connecting eastern and western Europe, including the routes between Poland, Galicia, Moravia, and Bohemia. At varying distances from her Russian frontier Austria has a line of mountains of great defensive strength. This is the Carpathian, which, extending inside the Austrian-Russian border line, is joined by the Transylvanian Alps and continues to form the south frontier of Austria. It would not be possible for the Russian invaders to menace Austria seriously until these mountains had been crossed. Russia, however, was menaced by the configuration of the German-Austrian frontier, with Poland open to invasion from three sides. Also, Austria and Germany had many strongly intrenched positions at strategical points covering all the chief lines of approach on their frontiers where the latter faced Russian territory. Besides being defended by artificial works, the frontier had natural defenses, such as lakes, swamps, and forests. All along the Russian-Austrian frontier, in fact, there exist such natural defenses against invasion. On the southern boundary of Poland the Russian army was held off by great bogs which cover from east to west a distance of about 250 miles. The only crossing was a single line of railroad, the one extending from Kiev to Brest-Litovsk. From a military viewpoint, these marshes divided the line in two parts, imperiling the situation of any fighting in front of them in case of defeat. They would offer no kind of sustenance to troops driven within them. Russia was not prepared to put into the field an army large enough to hold the entire line from the Baltic to the Rumanian frontier, approximately 1,000 miles, and there was no time, if part of the German forces were to be diverted from the western front, to raise such forces and equip them.